Property tycoon Sohel Rana was arrested as he attempted to flee to India and will face charges over the ruined eight-storey Rana Plaza, which like many other structures around the capital Dhaka violated the building code.
"He has been arrested and will be tried," the country's deputy home minister Shamsul Haque Tuku told reporters, referring to Rana, who is reportedly a ruling party official.
Amid the rubble, hundreds of rescuers continued the grim and painstaking task of searching for survivors with another two people pulled out alive after daybreak 100 hours after the collapse.
The focus will soon turn from one of rescue to clean-up, with the ever-growing stench of decomposition indicating many more bodies will be found once heavy lifting and earth-moving equipment gets to work.
"We have moved heavy equipment to the site but are still waiting for the clearance from the rescue workers inside the wreckage that no one is trapped alive," national fire chief Ahmed Ali told AFP at the scene.
Rescuers have been using only hand tools such as cutters and drills, fearing the use of cranes would jeopardise the chances of survival of anyone still clinging on four days after the accident on Wednesday morning.
The tragedy has once again focused attention on the poor safety conditions in the $20 billion Bangladeshi garment industry, which is the world's second biggest after China, supplying many big Western clothing brands.
Britain's Primark and Spain's Mango have acknowledged their products were made in the block, while an AFP reporter found shirts labelled "United Colors of Benetton" in the debris.
The Italian group has denied having a supplier in the building.
The accident has prompted fresh accusations from activists that Western firms place profit before safety by sourcing their products from a country where textile workers often earn less than $40 a month.
Protesters holding signs reading "Love Fashion Hate Sweatshops" and "Primark's Shame" picketed Primark's flagship store in London on Saturday.
As outrage over the country's worst industrial disaster spread at home and abroad, police have stepped up efforts to find the accused and border officials have been put on the highest alert.
Building owner Rana was detained at Bangladesh's main border crossing with India on Sunday while police were also hunting for Spanish entrepreneur David Mayor, whose manufacturing company operated from Rana Plaza.
Mayor, who spoke to AFP in 2009 for a story on ethical manufacturing in Bangladesh, co-owns Phantom-Tac, which he said was run with a strong "social concern".
Three factory owners have so far been arrested. They face a maximum five years in jail over charges of "causing death due to negligence", police say.
The case was filed after survivors told police how managers had forced them to return to work on Wednesday despite an evacuation the day before when cracks appeared on the outside of the building.
Senior investigating officer Kaiser Matubbor said two municipal engineers who gave the building the all-clear after an inspection on Tuesday were also arrested and could face charges of death due to negligence.
Deputy administrator of Dhaka district, Zillur Rahman Chowdhury, told AFP that the "death toll is now 376", with more than 2,400 people rescued alive since Wednesday.
Hundreds of relatives of missing workers again gathered at the site to watch as bodies were pulled from the debris and laid on a school playground for identification.
As the cranes prepared to get to work, hope was turning anger amid criticism of the slow pace of efforts, with some experts decrying a lack of coordination in the operation.
Expert Mehedi Ahmed Ansari, a professor of civil engineering at Bangladesh University of Engineering and Technology (BUET) also said that Bangladesh could have asked for foreign help.
"The methodology is fine, but they lacked proper coordination. Also, since we don't have any experience in this kind of rescue operation," he told AFP.
With many of Bangladesh's 4,500 factories shut due to protests, bosses declared holidays on Saturday and Sunday.
Several thousand garment workers protested on Friday and Saturday near the disaster site but they were dispersed by police firing rubber bullets and tear gas.